BIRDS TAILS AS SIGNALING DEVICES - MARKINGS, SHAPE, LENGTH, AND FEATHER QUALITY

While exaggerated length and ornamental shapes are confirmed sexually selected tail traits in birds, the signal function of tail markings ha s received less study. Signal roles for tail markings as amplifiers of length, shape, and feather quality are discussed, and the role of tai l markings as feather-quality handicaps is proposed: absence of melani n increases damage and abrasion. Predicted correlations of tail markin gs with other tail traits are derived for these signal roles. A compar ative study of the relationships between these rail traits in an entir e avifauna, the western Palearctic, tested the predictions. Tail displ ays were present in nearly 80% of species, associated with greater lon g-tailedness, but nor all displayed tails had markings or ornamental s hape. The incidence of marks across tail shapes and the combinations o f marks indicate that tail markings act as handicaps or amplifying han dicaps of tail feather quality. Tail elongation and ornamental shapes could act as additional handicaps of feather quality-that is, they cou ld be multipurpose signals. Incorporation of revealing indicators such as feather damage and associated handicap and/or amplifying traits ma y allow a reduction in the cost of signaling while maintaining signal reliability and, hence, influence sexual selection in complex signalin g systems.